Re: [BISECTED REGRESSION] b43legacy broken on G4 PowerBook

From: Larry Finger
Date: Sat Jun 08 2019 - 18:24:03 EST

On 6/7/19 12:29 PM, Christoph Hellwig wrote:
I don't think we should work around this in the driver, we need to fix
it in the core. I'm curious why my previous patch didn't work. Can
you throw in a few printks what failed? I.e. did dma_direct_supported
return false? Did the actual allocation fail?

Routine dma_direct_supported() returns true.

The failure is in routine dma_set_mask() in the following if test:

if (!dev->dma_mask || !dma_supported(dev, mask))
return -EIO;

For b43legacy, dev->dma_mask is 0xc265684800000000.
dma_supported(dev, mask) is 0xc08b000000000000, mask is 0x3fffffff, and the routine returns -EIO.

For b43, dev->dma_mask is 0xc265684800000001,
dma_supported(dev, mask) is 0xc08b000000000000, mask is 0x77777777, and the routine returns 0.

Thus far I have not found what sets the low-order bit of dev->dma_mask. Suggestions are welcome.

These tests have all been with your patch that sets ARCH_ZONE_DMA_BITS to 30.